1. Field of the Invention
This invention relates to the cutting of one or more circumferential grooves or threads, principally the former, in an interior bore of a workpiece. It is particularly useful for efficiently cutting a plurality of such grooves, or partial circumferential grooves, in a thin-walled or otherwise relatively fragile workpiece, where other modes of forming the grooves might result in the application of more heat or force than the workpiece can withstand.
The cutting of one or more circumferential grooves in an interior bore of a workpiece is usually accomplished by inserting a tool into the bore and forming each groove separately, stepping the tool axially between cuts. This is time consuming and permits tolerances to build up from one cut to the next so that the overall dimensional tolerance, unless very large, is difficult to maintain.
Various forms of rotary cutters and hobs have been used to form both external and internal threads. The formation of internal threads, however, is usually limited to the end regions of the workpieces due to constraints imposed by the overall geometry of the cutter and the cutting machinery.
Groove cutting machinery for this purpose also usually generates a relatively large chip which, while it can be disposed of in the case where only one groove at a time is formed, could not readily be disposed of if all of the grooves were to be formed at the same time, particularly where the internal bore of the workpiece is narrow.
2. Description of the Prior Art
U.S. Pat. Nos. 188,405; 425,372; 1,232,099; and 3,355,752 show various forms of cutting tools for cutting internal threads in which the teeth are separated by gullets. In all of these tools the entire circumference of the cutter engages the interior surface of the workpiece at the same time. There is no teaching that these tools or modifications thereof would be useful for producing grooves, as opposed to threads, on an internal surface.
U.S. Pat. Nos. 1,137,408 and 3,353,198 show rotary cutting tools held at both ends. However, they do not show machines in which the cutter engages the interior of a workpiece along a line, as does applicant's, nor do they teach rotation of the workpiece to complete the formation of the interior grooves.
U.S. Pat. Nos. 1,427,169, 1,611,122 and 1,588,003 show thread milling machines in which the workpiece as well as the cutting tool is rotated. U.S. Pat. Nos. 1,427,169 and 1,588,003 refer to the cutting of internal threads, but the disclosed machines are limited to forming such threads only near the ends of the workpiece. U.S. Pat. No. 1,611,122 teaches a device in which one rotation of a pipe is made to complete a threading operation, however, the thread is applied to the exterior of the pipe, not the interior, and the machine would not be capable of cutting such an internal thread.